This invention relates to non-burning foams that do not smoke when exposed to fire.
In the past, various additives have been included in polymer compositions to impart flame resistance and to reduce smoke emissions under conditions of fire. Such known additives include antimony trioxide and stannic oxide in ABS/PVC polymer blends.
Conventional fire-resistant polyurethanes contain phosphorous and/or halogen-containing compounds as additives. These additives are very expensive and corrosive. Other known additives include organic amine-metal complexes, such as alkoxymethylmelamine.
Other known compositions include rigid polyurethane foams to which melamine powder has been added in an effort to impart flame resistance while reducing smoke emission. In these known polyurethane foams, the melamine is believed to act merely as a filler-like material. However, it has been observed that these melamine-containing polyurethane foams suffer from several drawbacks. They exhibit, for instance, unsatisfactory flame resistance and smoke emission characteristics when exposed to fire. Additionally, when these foams contain large amounts of melamine, for instance, equal amounts by weight of the melamine filler and polyol component, these foams exhibit only limited flame resistance properties at the expense of useful processing, mechanical and other commercially attractive properties.
Conventional foams prepared from benyzlic ether-linked phenolic resins and isocyanates also suffer from several drawbacks. For example, it has been observed that such foams have moderate to extreme friability and only slight frame resistance. Additionally, such foams tend to emit free formaldehyde even after full curing. This poses health hazards and presents difficulty in complying with health regulations. The formaldehyde emission problem has added another roadblock to the effective commercialization of these foams.
Attempts to overcome these drawbacks include the use of a combination of basic tertiary amine catalysts in small amounts with certain specific and preferred blowing agents such as dichlorodifluoromethane and chloromethane. Such attempts have been limited in application to tertiary amine catalysts and certain preferred blowing agents, but have not met with any success. Such foams are not a commercially useful product.
According to the present invention, a three-dimensional cross-linked foamed reaction product of melamine, a di- or polyisocyanate and an ether-linked phenolic resin overcomes these drawbacks. Such a foamed product, a thermoset resin, is prepared in an anhydrous foaming process. The advantages of the foam of this invention are not dependent on the use of any particular blowing agent but are somewhat dependent on the particular catalyst system used. The resulting foam product is non-burning and essentially non-smoking under fire conditions and exhibits, for example, excellent compressive strength characteristics while being virtually non-friable.